Description

The objective of this failure is to identify examples of markup errors in element tags that could cause assistive technology to be unable to generate a satisfactory model of the page. Different user agents may implement different heuristics to recover from errors, resulting in inconsistent presentations of the page between user agents.

Some common types of problems with start and end tags that lead to this failure condition (though this is not an exhaustive list):

Opening and closing tags that are missing the opening < and closing > brackets.

Closing tag missing the initial / to indicate it is a closing tag.

Attribute values that have an opening quote but not a closing quote. Attribute values must be either fully quoted or, in some markup languages, may be unquoted.

Lack of whitespace between attributes.

Unquoted attribute values that have whitespace in the value.

Failure to provide a closing element tag for elements that do not accept empty-element syntax.

Examples

Failure Example 1: Missing angle brackets in XHML

The following code fails because the opening tag is missing an angle bracket, and the intended boundary of the tag is unclear.

Example Code:

<p This is a paragraph</p>

Failure Example 2: Missing slash on closing tag in XHTML

The following code fails because the closing tag is missing the slash, making it look like it is in fact another opening tag.

Example Code:

<p>This is a paragraph<p>

Failure Example 3: Unbalanced attribute quoting

The following code fails because the attribute value is missing the closing quote, which makes the boundary of the attribute-value pair unclear.

Example Code:

<input title="name type="text">

Failure Example 4: Lack of whitespace between attributes

The following code fails because the there is not whitespace between attributes, which makes the boundary between attribute-value pairs unclear.

Example Code:

<input title="name"type="text">

Failure Example 5: Unquoted attribute with whitespace value

The following code fails because an attribute value is not quoted and contains whitespace, which makes the boundary of the attribute-value pair unclear.

Example Code:

<input title=Enter name here type=text>

Failure Example 6: Missing end tags in XHTML

The following code fails because the closing tag of the first paragraph is missing, making it unclear whether the second paragraph is a child or sibling of the first.